Stainless steel and articles



United States Patent 3,282,684 STAINLESS STEEL AND ARTICLES Paul M. Allen, Middletown, Ohio, assignor to Armco Steel Corporation, Middletown, Ohio, a corporation of Ohio No Drawing. Filed July 31, 1963, Ser. No. 299,110 8 (Ilaims. (Q1. 75-125) My invention relates to stainless steel and more especially to a stainless steel suited to a variety of indoor and outdoor applications.

One of the objects of my invention is the provision of a stainless steel which is comparatively inexpensive in that it employs a minimum of expensive alloying ingredients; which steel readily lends itself to hot-working and then to cold-Working at minimum cost in that it possesses a low work-hardening rate and permits maximum coldreduction without necessity for intermediate anneal; and which cold-worked steel readily lends itself to a variety of forming and fabricating operations.

Another object is the provision of hot-rolled sheet, strip, wire and like products as well as the provision of cold-rolled sheet and strip of cold-drawn wire and the like, all at minimum cold-Working costs; which coldrolled sheet, strip, wire and like products, as Well as hotrolled products where desired, lend themselves to a variety of forming and fabricating operations such as bending, drawing, deep-drawing, spinning, and the like, as well as shearing, cutting, sawing and drilling; and which products readily may be brazed and welded as in the fabrication of a host of articles of ultimate use.

A further object is the provision of a variety of stainless steel articles of ultimate indoor use such as kitchen sinks, trim, fittings, and the like, having eye appeal yet being adapted to withstand the corrosive action of foodstuffs commonly encountered in kitchen, bath and other home and industrial usage, as well as the provision of a variety of articles of outdoor use, notably automobile trim, wheel covers, bumpers and like bright metal parts appealing to the eye, yet functional, and well adapted to withstand the conditions encountered in actual practical use such as the dust and heat of summer, the cold of winter and the snow, sleet, ice and salt thrown up from the road in winter driving, as well as the salt atmosphere of the seashore, all without objectionable pitting, corrosion, rusting and discoloration.

Other objects of my invention will be apparent, or will be pointed to, during the course of the description of my invention which follows.

Accordingly, my invention will be seen to reside in the combination of elements, the composition of ingredients and the relation between the same, and in the products and articles of use embracing the same, all as described herein, the scope of the application of which is set forth in the claims at the end of this specification.

Now in order to gain a better understanding of certain features of my invention, it may be noted at this point that the well known type 430 stainless steel (analyzing carbon .12% max., manganese 1.00% max, silicon 1.00% max, phosphorus .04% max, sulphur .03% max, chromium 14.00% to 18.00%, and remainder iron) has been well received in the art. Cold-rolled and annealed sheet and strip of the type 430 steel has a tensile strength of about 75,000 p.s.i., a yield strength of about 45,000 p.s.i., an elongation in 2" of about 25%, and a hardness of about Rockwell B80. While this steel lends itself to common working and forming operations, the corrosionresisting characteristics of the metal leave much to be desired.

In the automotive industry the type 430 was widely employed in bright metal parts. Under severe weather 3,282,684 Patented Nov. 1, 1966 conditions encountered in actual use, however, these bright metal parts lost their lustre, became pitted and were subject to the development of a red rust. And the eye appeal of bright metal was quickly lost and the general appearance of the automobile immediately sulfered. The automotive industry turned to other metals.

Aluminum and its various alloys, While olfering promise, lacked the hardness and strength necessary. The metal in the form of automobile body trim was easily dented and appearance sufifered as a consequence. Moreover, the metal lacked lustre and generally left much to be desired.

Now the type 301 grade of stainless steel (analyzing carbon 0.15% max., manganese 2.00% max, silicon 1.00% max, phosphorus .045 max, sulphur 03% max, chromium 16.00% to 18.00%, nickel 6.00% to 8.00%, and remainder iron) has been rather well received in the art for a variety of applications. The same may be said for the type 32 (analyzing carbon 0.15% max, manganese 2.00% max., silicon 1.00% max, phosphorus .045 max, sulphur .03% max., chromium 17.00% to 19.00%, nickel 8.00% to 10.00%, and re mainder iron).

Cold-rolled sheet and strip of the type 301 steel in annealed condition has a tensile strength of about 110,000 p.s.i., a yield strength of about 40,000 p.s.i., a 2" elongation of about 60%, with a hardness of about Rockwell B85. The type 302 cold-rolled and annealed sheet and strip has a tensile strength of about 90,000 p.s.i., a yield strength of about 40,000 p.s.i., a 2" elongation of about 50%, and a hardness of about Rockwell B85.

The type 301 steel is soft, ductile and readily workable and formable. Unfortunately, it is expensive because of the high cost of certain of the alloying ingredients. Moreover, it is costly to convert from hot-rolled strip to thin flat-rolled products, largely as a result of the inherent characteristic of hardening during working; in the cold-rolling operation, intermediate annealing of the metal becomes necessary as a result of the development of hardness values unacceptable for further working. Such intermediate annealing is both time-consuming and costly, particularly in that it interrupts progress of the conversion operation. The type 302, although of low wark-hardening rate, is evenmore expensive than the type 301.

A further known stainless steel is the chromium-nickelcopper steel as described, for example, in the Bloom- Clarke U.S. Letters Patent 2,687,955 of August 31, 1954, entitled, Cold-Workable Stainless Steel and Articles. While that steel possesses a compartively low workhardening rate it, too, is comparatively expensive. And, moreover, at the higher nickel levels, when subjected to drastic deformation, as in severe deep-drawing, is in-, 'clined to local stressing and resultant irregularity in section.

Accordingly, one of the principal objects of the present invention is the provision of a stainless steel of desired corrosion-resisting characteristics which employs a minimum of expensive alloying ingredients in its composition; which handles well in the furnace and teeming ladle; which works down from ingot to billet to sheet, strip, wire and the like, with ease; and which then readily lends itself to cold-reduction up to some to without necessity for intermediate anneal as in the production of coldrolled sheet, strip and cold-drawn wire; which sheet, strip, and Wire are ductile and readily forrnable by a variety of forming operations.

Referring now more particularly to the practice of my invention, I provide a stainless steel which possesses the corrosion-resisting characteristics of the types 301 and 302 steels at substantially lower cost of ingot, however, and at susbtantially lower cost of converted product, that is,

hot-rolled sheet, strip, wire and the like, as well as coldrolled sheet, strip, wire, and other cold-worked products. The savings in ingot costs derive from the saving in the cost of alloying ingredients, compared to type 302, and the saving in the cost of conversion derives from a shorter routing of the metal through the mill, this being permitted because of a lowering of the work-hardening rate characterizing the type 301.

The steel of my invention essentially consists of carbon up to .15 preferably in the amount of about .04% to 15%, manganese in the amount of .40% to 2.00%, silicon in the amount of .15 to 1.00%, chromium in the amount of 16.0% to 19.0%, nickel in the amount of 5.5% to 8.0%, copper in the amount of .5 to 3.5%, nitrogen in the amount of .04% to .10%, and remainder essentially iron. The steel of my invention is in every sense critical in its composition for I find that with any substantial change in the balance of the ingredients of the composition one or more of the desired properties are lost.

As to the carbon content of my steel, I find that the .15 figure approaches the limit of solubility for normal annealing and cooling rates. A carbon content exceeding .15 is inclined to give a sensitized structure with risk of a severe loss of corrosion resistance. The carbon content preferably, however, is maintained at a value not A copper content short of the 1.0% figure and certainly anything short of the .5% figure does not effectively lower the work-hardening rate of the metal. And a copper content exceeding 3.0%, and certainly one exceeding 3.5%, is likely to result in hot-rolling difficulties, notably the likelihood of the metal to break in the hot-mill, since 3.5% is about the limit of solubility. Moreover, I feel that with an excess of copper, the corrosion resistance of the steel is inclined to suffer. The preferred copper range is 1.75% to 2.25%.

And I find that nitrogen is an essential ingredient in the steel of my invention, this in the amount of .04% to .10% Nitrogen, I find, helps to stabilize the metal. Less than .04% nitrogen is ineffective and at least .05 is preferred in order to safely assure a freedom from delta-ferrite formation. Nitrogen in an amount exceeding .10% results in the possibility of developing ingot unsoundness. Therefore, a nitrogen content of about .05 to .07% is used for best results.

The particular steel according to my invention in which there is had the best combination of desired properties, that is, minimum ingot cost, minimum mill cost, along with maximum resistance to corrosion and maximum formability, is set out below in Table I, this presenting the melting range of the steel as well as the aim analysis:

TABLE I.-PREFERRED STEEL OF INVENTION 0 Mn P s Si Cr Ni Cu N Range .05/.0s 125/175 .03/Max. .02/Max. .40/.75 17.25 1s.00 6.25/6.75 1.75/2325 .os m Aim .07 1 .50 Low Low .50 17 .60 6 .50 2 .00 .06

Remainder essentially iron. exceeding .08% in order to assure a minimum of work In the melting of the steel of my invention an electric hardening and especially a value of .04% to .08% since at least .04% carbon is desired for its stabilizing effect. A preferred range is .05% to .08%.

The manganese content of my steel similarly is critical in that I find a manganese content less than about .40% fails to support the required nitrogen content more fully dealt with below. And manganese exceeding 2.00% gives little benefit and increases the cost as well. The man ganese content, therefore, amounts to .40% to 2.00%, or even about .5 to 2.00%, and more particularly about 1.25% to 1.75%.

The silicon content of my steel is critical; at least .15% is necessary to assure an ease of furnacing and teeming, while silicon exceeding 1.00% is objectionable because of its ferrite-forming tendencies. An excess of silicon requires additional nickel at, of course, additional expense, to compensate for the same. I therefore employ a silicon content of .15 to 1.00%, this preferably amounting to about .40% to .75%. 1

In the steel of my invention the chromium content amounts to 16.0% to 19.0%, this being critical, too. Preferably, this ranges from 16.0% to 18.0%. A chromium content lower than 16.0% results in a loss of corrosionresistance and, moreover, it is inclined to. result in an objectionable increase in the work-hardening rate of the metal. A chromium content in excess of 19.0% is not acceptable because it results in an excessive delta-ferrite content at ingot-rolling temperatures. Desired results are had with a chromium content of 17.25% to 18.00%.

A nickel content of 5.5 to 8.0% is required in my steel, this preferably amounting to about 6.0% to 8.0%. With a nickel content short of about 5.5 the workhardening rate becomes excessive and in addition, there is an inclination to develop delta-ferrite. With a nickel content exceeding 8.0% the cost becomes prohibitive. A nickel range of 6.25% to 6.75% gives best results.

Copper is an ingredient essential to the steel of my invention. This is employed in the amount of .5% to 3.5 Actually, I employ a copper content of about 1.0% to 3.5%, more preferably about 1.0% to 3.0%.

arc furnace commonly is employed. Where desired, however, it will be understood that the steel may be vacuum melted or otherwise melted to specification. However melted, the steel handles well in the furnace and in the pouring ladle. The steel in the form of ingots is converted into slabs, blooms and billets. It is then reheated and hot-rolled into sheet, strip, wire and the like. The steel works well in the hot mill.

Conveniently, the hot-rolled metal comes off the mill in coils which may be annealed and pickled, or merely pickled and then cold-worked to specification. Coldrolled sheet and strip is had through a short routing through the mill, that is, without necessity for intermediate anneal. The amount of cold-reduction commonly approaches 75%. Similarly, the hot-rolled wire is colddrawn. And here again, the drawing operation is simply and inexpensively effected without necessity for intermediate anneal, the amount of cold-reduction being up to about 75 As illustrative of the steel of my invention, I present below in Tables II and 111, respectively, the chemical analyses and the mechanical properties of some 17 steels, 10 of these being the steels of my invention:

TABLE IL-CHEMICAL ANALYSES 0F SEVENTEEN STEELS Code No. 0 Mn Si Cr Ni Cu N *Steels of present invention.

The steels of Table II in the form of ingots were hotrolled to a thickness of about .100" from an ingot temperature of 2150 to 2200 F., the metal then being in the form of strip. This strip was annealed and pickled at about 2000 F. and cold-rolled to .025" thickness. Test specimens were taken for the steel at zero cold-reduction (.100" thickness) and at 75% cold-reduction (.025" thickness). The mechanical properties of the two test specimens for each steel are reported below in Table III, this presenting .2% yield strength, tensile strength and the percent elongation in 2":

TABLE III.-MECHANICAL PROPERTIES OF STEELS OF OF TABLE II IN THE FORM OF STRIP WITH 0 REDUC- TION AND WHEN COLD-REDUCED 75% Percent .2% Y.S., Ten. Str. Percent Code No. Cold- K s.i. K s.i. Elong.

Reduction in 2 *Steels of present invention.

It will be seen from the information presented in Tables II and III above that steel L1 actually is a standard 188 chromium-nickel stainless steel (type 302) this being used as a basis for comparing the work-hardening rates of certain of the steels of my invention. The steels D1, D2, D3, E3, K1 and N1 are all low carbon steels of compositions likewise used for comparative purposes. Note that the steels D1, D2 and D3 are of increasing manganese contents and nitrogen contents. The steels E3 and N1 are of virtually the same composition as the steel D1. And the steel K1 is of about the same composition as the steel D2.

Now in the cold-reduction of the various groups of the steels presented above, no attempt was made to control the temperature of the metal except to retain as much as possible the heat which developed .during the coldworking. It is particularly significant that in the steels outside the compositon range of the steels of interest there is a wider variation in properties of steels of like analyses than there is in the steels of my invention. Note, for example, that of the three steels D1, E3 and N1, these being of generally like composition (about 1% manganese, 17.8% chromium, 7.7% nickel, with low carbon, silicon and nitrogen contents, incidental amounts of copper and molybdenum, and remainder iron) the .2% yield strength of D1 amounts to about 225 kilo pounds per square inch for the 75% cold-reduction, while E3 amounts to about 219K s.i. and N1 amounts to 196K s.i. And note also that the yield strength developed in all three steels was much greater than that developed in the standard 188 chromium-nickel steel, sample L1, this, for a cold-reduction of 75 having a yield strength of about K s.i. A like difference is found in the tensile strength figures, these ranging from about 240K s.i. for sample D1 to 211K s.i. for sample N1; the 18-8 chrornium-nickel sample L1 has a tensile strength of only 207K s.i All reflect a difference in work-hardening rate, the higher work-hardening rates being indicated by the high yield and tensile figures and the lower hardening rates being indicated by the lower figures.

In contrast with the hardness and strength developed in the cold-working of the steels presented for comparison purposes, the specific steels of my invent-ion for the 75% cold-reduction developed a yield strength of only about 183K s.i. and 170K s.i., respectively, and tensile strength of 199K s.i. and 182K s.i, for samples E2 and E1, these being of the 1% manganese and 7.7% nickel levels with copper contents of 1.50% and 2.85%, respectively, and nitrogen about .04%, this as compared with the E3 steel with incidental copper having a .2% yield strength of about 219K s.i. and tensile strength of 233K s.i. The pronounced effect of the copper variation is immediately apparent.

Similarly, with the steels of a manganese level of 1.5% or thereabouts with cold-reduction of 75 there is had a .2% yield strength of about 193K s.i. and a tensile strength of 209K s.i. for sample P2 with higher nickel content (nickel about 7%, copper about 1.5% and nitrogen about 09%) and a yield strength of 174K s.i. and tensile strength of 192K s.i. for sample P3 of the higher nickel and higher copper content (nickel about 7%, copper about 2.4% and nitrogen 09%).

And for the two steels I1 and 12 of dilfering but high manganese levels and like nickel, copper and nitrogen levels (about 1.5% manganese, 7.7% nickel, 1.5% copper and .06% nitrogen for the one, and about 2% manganese, 7.7% nickel, 1.5% copper and .06% nitrogen for the other) the .2% yield strength figures for the 75% reduction steel, respectively, are about 184K s.i. and 179K s.i., which tensile strengths of 202 and 196K s.i. The steel K1 outside the scope of the present invention, at a 1.5% manganese level and 7.7% nickel, with incidental copper and .04% nitrogen, has a yield strength, for the 75 reduction, amounting to about 204K s.i with a tensile strength of 220K s.i.

And finally, for the samples M1, M2 and M3, the former being of 1% manganese level and the other two being of the 1.5%, with about 6.2% nickel, copper about 2% (M1 having about 1% manganese, 6.2% nickel, 1.8% copper, .04% nitrogen; the M2 having about 1.5 manganese, 6.2% nickel, 1.8% copper and .06% nitrogen; and the M3 having about 1.5 manganese, 6.5% nickel, 2% copper and .06% nitrogen) respectively develop yield strengths at the 75 cold-reduction of about 186K s.i., 181K s.i. and 177K s.i. and tensile strengths of K s.i., 195K s.i. and 192K s.i. These are seen to contrast well with the sample N1 of higher nickel content but of only incidental copper content (about 1% manganese, 7.8% nickel, incidental copper and .04% nitrogen) which develops a yield strength of 196K s.i. and a tensile strength of 211K s.i. And the reduced yield and tensile strengths of sample M2 as compared with the values for sample M1 reflect the lowering of working-hardening rate had with slight increases in manganese and nitrogen contents.

It will be seen that the specific steels of the present invention develop a .2% yield strength and tensile strength, at 75% cold-reduction, which do not exceed about 200K s.i., irrespective of variations of manganese content and at a substantial savings in nickel over and above that required in the 18-8 chromium-nickel stainless steel, the developed yield strengths actually ranging from 170 to 193K s.i., and the tensile strengths from 182 to 209K s.i. All of these steels essentially employ copper as a purposeful addition and in substantial amount, this along with manganese and nitrogen. The steels with but incidental copper content (D1, D2, D3, E3, K1 and N1) except for the standard 18-8 chromium-nickel stainless steel (L1) develop yield strengths and tensile strengths, at 75% cold-reduction, which are objectionably high, irrespective of manganese and nitrogen additions. These range from about 196K s.i. to 225K s.i. for yield strength and 211K s.i. to 240K s.i. for tensile strengths.

Thus it will be seen that I provide in my invention a stainless steel of good corrosion-resisting characteristics, employing a minimum of expensive alloying ingredients. The steel is economically melted in the electric arc furnace. It furnaces Well and teems well. Moreover, because of its comparatively low work-hardening rate, this as compared to the Well known type 301 chromium-nickel stainless steel and a variety of other chromium-nickel steels, the steel of my invention may be cold-worked, as by cold-rolling or cold-drawing, to a reduction in area amounting to about 75% or more without requiring an intermediate annealing operation. The production of cold-rolled sheet and strip, and cold-drawn wire from hot-rolled sheet, strip and Wire thus is achieved at minimum expense.

The steel and sheet, strip, wire and the like of my invention conveniently is supplied the trade in an annealed and pickled or in a bright annealed condition at significantly lower cost. These mill products well lend themselves to fabrication, as by bending, drawing, deep-drawing and other forming operations commonly practiced on the well known 18-8 chromium-nickel grade of stainless steel. Moreover, these products may be sheared, cut, sawed, drilled and the like, as Well as brazed and welded, as in the production of a variety of articles of ultimate use such as automobile body trim, window frames, door frames, wheel covers, bumpers, and the like, where bright metal and appeal to the eye is desired. The steel and articles well resist the attack of the salty atmosphere encountered at the seashore as well as the salt thrown up from the streets, roads and highways during the winter when salt commonly is employed to etfect de-icing. And the steel of my invention is well adapted to withstand the abuse commonly encountered in every-day automobile driving and parking.

Other articles of ultimate use fashioned of my steel include kitchen sinks, kitchen and bathroom fittings, trim, and the like, where corrosion-resistance and eye appeal are required. The steel is well calculated to resist the attack of various mild acids, bases and salts encountered in a number of commercial and industrial uses.

Many embodiments of my invention will occur to those skilled in the art to which the invention relates, and many variations will occur with respect to the embodiments herein disclosed. Therefore it will be understood that all such matter described herein is merely illustrative; it is not to be taken as a limitation.

I claim as my invention:

1. Stainless steel essentially consisting of carbon up to about .15 manganese .40% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel 5.5% to 8.0%,

copper .5% to 3.5%, nitrogen' .04% to .10%, and remainder essentially iron.

2. Stainless steel essentially consisting of carbon up to about .08%, manganese .40% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to about 18.0%, nickel about 6.0% to 8.0%, copper about 1.0% to 3.0%, nitrogen .04% to .10%, and remainder essentially iron.

3. Chromium-nickel-copper stainless steel of low workhardening rate and essentially consisting of carbon about .04% to .15%, manganese about .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel about 6.0% to 8.0%, copper .5% to 3.5%, nitrogen .05% to .10%, and remainder essentially iron.

4. Chromium-nickel-copper stainless steel of low workhardening rate and essentially consisting of carbon about .04% to .08%, manganese about .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 18.0%, nickel 5.5% to 8.0%, copper about 1.0% to 3.0%, nitrogen .05% to .10%, and remainder essentially iron.

5. Chromium-nickel-copper stainless steel of low workhardening rate and essentially consisting of carbon about .05% to .08%, manganese about 1.25% to 1.75%, silicon about .40% to .75%, chromium about 17.25% to 18.00%, nickel about 6.25% to 6.75%, copper about 1.75% to 2.25%, nitrogen about .05% to .07%, and remainder essentially iron.

6. Hot-rolled chromium-nickel-copper stainless steel sheet, strip, wire and the like of low work-hardening rate and essentially consisting of carbon about .04% to .15%, manganese about .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 18.0%, nickel about 6.0% to 8.0%, copper about 1% to 3.0%, nitrogen .05 to .l0-%, and remainder essentially iron.

7. Cold-rolled chromium-nickel-copper stainless steel sheet, strip and like products having a low work-hardening rate and essentially consisting of carbon up to about .08%, manganese about .5% to 2.00%, silicon .15% to 1.00%, chromium 16.0% to 19.0%, nickel about 6.0% to 8.0%, copper about 1% to 3.5%, nitrogen .05% to .10%, and remainder essentially iron.

8. Cold-worked chromium-nickel-copper stainless steel products having a low work-hardening rate and essentially consisting of carbon about .04% to .15%, manganese .40% to 2.00%, silicon .15 to 1.00%, chromium 16.0% to 19.0%, nickel 5.5% to 8.0%, copper about 1.0% to 3.5%, nitrogen .04% to .10%, and remainder essentially iron.

References Cited by the Examiner UNITED STATES PATENTS 2,482,098 9/1949 Clark l25 2,687,955 8/1954 Bloom 75125 3,183,081 5/1965 Clark 75l25 DAVID L. RECK, Primary Examiner.

P. WEINSTEIN, Assistant Examiner. 

1. STAINLESS STEEL ESSENTIALLY CONSISTING OF CARBON UP TO ABOUT .15%, MANGANESE .40% TO 2.00%, SILICON .15% TO 1.00%, CHROMIUM 16.0% TO 19.0%, NICKEL 5.5% TO 8.0%, COPPER .5% TO 3.5%, NITROGEN .04% TO .10%, AND REMAINDER ESSENTIALLY IRON. 